In Nov 2013 I wrote an article about my final 12-600 acquisition. At that stage I had 5 12-600 but also had a ref 3433 which had a 27-460 movement rather than a 12-600, the equivalent watch being the 2551.

Well after 4 years, a 2551 has now materialised in my collection and I feel that I can now close the chapter on this part of my collection.

The only one I do not own is the ref 3403, a rather small automatic watch (32mm) similar in size to the ref 96.

So here we have the two watches side by side:

Aside from the crown 3433 has a regular crown, whereas the 2551 has the famed double PP crown.

The dials are slightly different in terms of colour- cream versus champagne.

So the only true difference is the engine or movement. The 3433 has the newer 27-460 and the 2551 has the legendary 12-600

Please note pics of 12-600 are from my 2540, but the 27-460 are stock pics from Google. My 3433 is in the vault.

Differences

1. Size -12-600 is 12 ligne or 28mm wide and 6mm thick, whereas the 27-460 is 27mm wide but a little thinner at 4.6mm.
2. This is due to the fact that the rotor assembly is different with a slightly flatter ball bearing
3. The beautifully guilloched gold rotor in the 12-600 which is hidden behind a solid case back is not present in the later 27-470. It still has a beautiful gold rotor but it is not decorated.
4. The balance spring also has a unique self-adjustable balance spring stud carrier which allows the spring to self-centre which is key to positional performance
5. The 27-460 all had the gyromax balance unlike some of the earlier models of the 12-600 which have a swan neck regulator
6. 30 jewels in 12-600 versus 37 in 27-460
7. The 27-470 had a date variation 27 -470M